Severe megaloblastic anemia in a patient receiving low-dose methotrexate for psoriasis.

Severe megaloblastic anemia with a normal white blood cell and platelet count developed in a patient with psoriasis vulgaris who was receiving long-term, low-dose methotrexate. We believe she had methotrexate-induced folate deficiency anemia with isolated inhibition of the erythrocytic bone marrow line. We review hematologic toxicity from low-dose methotrexate. Physicians caring for patients who receive low-dose methotrexate should be aware that an increase in the erythrocyte mean corpuscular volume may be a useful indicator of folate deficiency and impending toxicity. In addition, folate supplementation may prevent this toxicity (even in patients who do not appear clinically to be folate deficient), although whether methotrexate efficacy diminishes is controversial.